Liquid crystal displays (LCDs) are commonly used as display devices for compact electronic apparatuses. This is because they not only provide good quality images with little power consumption, but they also are very thin. The liquid crystal in a liquid crystal display does not emit any light itself. The liquid crystal has to be lighted by a light source so as to clearly and sharply display text and images. Thus, a backlight module is generally needed for a liquid crystal display.
Referring to FIG. 5, a typical LCD device 5 includes a liquid crystal panel 50, and a backlight unit 51 for providing uniform light for the liquid crystal panel 50. The backlight unit 51 includes a plastic frame 52, a diffusion film 53, a prism film 54, a light guide plate 56, two light sources 57, and a reflective film 58. Each light source 57 includes an elongated lamp 571 such as a cold cathode fluorescent lamp (CCFL), and a lamp cover 572 surrounding three sides of the lamp 571. The lamp cover 572 is generally U-shaped, and includes an upper plate (not labeled), a lower plate (not labeled) opposite to the upper plate, and a side plate (not labeled) perpendicularly adjoining both the upper plate and the lower plate.
The light guide plate 56 includes two light incident surfaces 561 at opposite sides thereof, a top light output surface 562 perpendicularly adjoining the two light incident surfaces 561, a bottom surface 563 perpendicularly adjoining the two light incident surfaces 561, and two other side surfaces (not labeled) perpendicularly adjoining the light output surface 562 and the bottom surface 563. The light sources 57 are disposed adjacent to the light incident surfaces 561, respectively.
Referring also to FIG. 6, the reflective film 58, the light guide plate 56, the diffusion film 53, and the prism film 54 are arranged in that order from bottom to top. A part of the upper plate and a part of the lower plate of each lamp cover 572 are attached to an edge portion of the light output surface 562 and an edge portion of the bottom surface 563, respectively. That is, the lamp covers 572 are clamped to two opposite sides of the light guide plate 56, respectively.
The prism film 54 and the diffusion film 53 are arranged on the light output surface 562, in that order from top to bottom. Edges of the two films 53, 54 are adjacent to edges of the upper plates of the lamp covers 572, respectively. The two films 53, 54 are very thin, and typically have a thickness of about 0.4 mm. When the lamps 571 work, the temperatures of the lamp covers 572 rise. Because the two films 53, 54 are very thin, they are liable to be affected by the high temperatures of the lamp covers 572 and become warped. Then when light transmits through the two films 53, 54, the display performance of the LCD device 5 is impaired.
What is needed, therefore, is a backlight module that can overcome the above-described deficiencies. What is also needed is an LCD device employing such a backlight module.